Women with inadequate health insurance have lower mammography rates than the general population. Finding successful strategies to enroll eligible women is an ongoing challenge for the National Breast and Cervical Cancer Early Detection Program. To test the effectiveness of a population-based strategy to increase mammography utilization among low-income underinsured women ages 40 to 64 years, a randomized trial was conducted to assess the effect of two mailed interventions on mammography utilization through Sage, the National Breast and Cervical Cancer Early Detection Program in Minnesota. Women (N = 145,467) ages 40 to 63 years [mean (SD), 49.7 (6.8)] with estimated household incomes below $50,000 (47.9% were <$35,000) from a commercial database were randomized to three groups: Mail, Mail Plus Incentive, or Control. Both the Mail and the Mail Plus Incentive groups received two simple mailings prompting them to call a toll-free number to access free manunography services. The Mail Plus Incentive intervention offered a small monetary incentive for a completed mammogram. After 1 year, both intervention groups had significantly higher Sage mammography rates than the Controls, and the Mail Plus Incentive group had a significantly higher rate than the Mail group. The Mail and Mail Plus Incentive interventions were estimated to produce increases in Sage screening rates of 0.23% and 0.75%, respectively, beyond the composite Control rate of 0.83%. Direct mail is an effective strategy for increasing manunography use through Sage. Coupling direct mail with an incentive significantly enhances the intervention's effectiveness. Direct mail should be considered as a strategy to increase mammography use among low-income, medically underserved women.